Torsion springs are typically constructed to provide a specified torsion force over a specified angle of rotation. Typically designs are based on coiled flat springs where the force is limited but the angle can be large or on large cross-section coil springs where the angle is limited but the force is large.
Difficulty arises where a large force and substantial angle of movement is required. Conventional solutions typically require a very heavy and large form of spring that allows the material of which the spring is constructed to stay within its limits of stress while achieving the necessary displacement. For example, to achieve a required force a spring may require a certain diameter of element and at a given diameter the element is coiled until there are sufficient turns to enable the required angle of movement to be possible without exceeding the material stress or strain limits. This results in a heavy and bulky solution.
When considering vehicle suspension systems, which are typically (though not exclusively) linear spring arrangements spring mass and volume become important due to the fact that often the suspension mass adds to the wheel unsprung mass and so has direct negative impact on the effectiveness and response of the dynamic behaviour of the suspension.
Torsion bar systems have been used to help alleviate this problem, but this solution carries the negative attribute of needing long lengths (often heavy though not part of the unsprung mass) of material in order to provide for the necessary stress and strain constraints of any chosen material.
In all the above examples the cost of the suspension system is relatively high and adds cost, complexity and mass to the vehicle.
One of the main problems with suitable spring materials is that they are either constrained with displacement if large force is required, for example various types of steel, or constrained with limited force if large displacement is required, for example plastics or composites. Additionally present vehicle suspension systems require additional devices to damp out oscillatory motion. These “dampers” (or shock absorbers) are typically fitted directly between a moving wheel axle and chassis of a vehicle. They take up further valuable space and add further cost and complexity to the suspension system.
The present applicant has identified the need for an improved torsion device that overcomes or at least alleviates problems associated with the prior art.